Much of Justice is about waiting: waiting without knowing why, waiting for an unknown deliverance. (Miri, the mother, seeks revenge but hasn't chosen a particular punishment.) Justice only comes to those who nobly wait.
On one level, the book is about the relationship between doctors and nurses. (Miri is a nurse, Renzo a doctor.) It's also about pignolia nuts, a food freely offered by the hills of Italy.
I would call Justice a "geographical love story" — the love between a writer and a landscape. Harrison expertly evokes the Calabria of 1948, a place trying to return to its ancestral sleep, but already bit by the vampire of modernity.
Carey knows what is a novel. Many of the works of fiction today are either genre or facile satires (the latter being the "hot" ones). This is an actual novel; in other words, the last line perfectly completes the logic of the book. The abstract title suggests Carey's ambition — to explain all justice, for all time. And he succeeds.
I just realized: "Vittorio" means "victory"!